Slack Passes 1.1 Million Daily Users, Hires Twitter Veteran As Head Of Platform

With more than one million people now logging in to swap messages with coworkers each day, Slack continues to grow at a heady pace. But as it increasingly focuses on the ecosystem of what other companies can do better by integrating their own products within Slack, CEO Stewart Butterfield is bringing in some major help.

Slack has tapped April Underwood to serve as its head of platform, the company announced Wednesday, to work with its growing network of partners through both APIs and deeper integrations. Underwood had spent nearly five years as director of product at Twitter until February and helped manage partnerships at Google earlier in her career.

"We are pinching ourselves frequently," says Butterfield. "Every Wednesday is our best Wednesday ever. Every Saturday is our best Saturday ever. And April's pretty rare in the sense that she's done business development and engineering. Twitter is a different kind of use case, but there's a lot of similarities in the nature of our APIs. So it's the ideal background."

More than 180 employees now work at Slack, which has built a fast-growing money-making operation alongside its free adoption. The company says it's making more than $25 million in annual recurring revenue after just a year off of 300,000 paid seats.

Underwood will be in charge of guiding Slack from just under 100 partner integrations, including Dropbox, Google Docs and Twitter, to a whole lot more. "The ideal case for us is that your use of Slack makes your use of all these other tools better for you," says Butterfield. "If you use Dropbox, using Slack should be way more useful. But it can be Box. It doesn't really matter to us which you use. Slack can make each slightly better."

How a Zendesk integration looks inside Slack.

Butterfield believes Slack represents a new way of working that encourages transparency and teamwork between employees, who can set specific work groups and flow in data from a range of sources to discuss and share without any outside noise. Where Slack can improve the most, he says, is in little inefficiencies that still exist in the young product, like the ability to invite people to a Slack team from its mobile app.

Though Slack has raised aggressively for such a young startup--its most recent funding round confirmed in April took in $160 million at a $2.8 billion valuation--Butterfield says Slack's not angling to tackle communications from one company to another, despite such interest. Do that, he says, and Slack would just become like LinkedIn, email or Skype, which are already noisy enough to make something internal like Slack a relief in the first place. He points to third-party projects like open-sourced Slackline to extend how Slackers can communicate across teams.